128 BOARD OF AGRICULTURE. [Pub. Doc. 



the domain of chemistry, and enter the domain of biology. 

 It is one of the greatest triumphs of science that we have 

 come to understand the profound and practically important 

 relation which certain microscopic forms of life inhabiting 

 the soil sustain to the fertility of our helds, — a relation 

 which has a vast significance to the human family. These 

 organisms are minute, — too minute to be seen by the 

 unaided vision ; but in a silent and unseen way they appear 

 to do a work which is second to none in its importance to 

 the farmer. For the purposes of a brief discussion I shall 

 classify these organisms according to function : — 



1. Those which cause chemical changes in the nitrogenous 

 constituents of the soil, both inorganic and organic. 



2. Those bacteria which, when associated with certain 

 agricultural plants, in some mysterious way through this 

 symbiotic relation confer the power upon these plants to 

 acquire atmospheric nitrogen. 



3. Those oro;anisms which, when not sustaining, so far 

 as is known, any relation to agricultm'al plants, cause the 

 soil to acquire nitrogen from the atmosphere. 



Speaking with regard to the first class of organisms, permit 

 me to state that their existence and office have been known 

 to us for some time. These are the forms of life which per- 

 form the valuable and necessary service of causing the other- 

 wise useless oro-anic nitrosfen to chano'e to the form of nitrous 

 or nitric acid, through m hat we know as an oxidizing process ; 

 or Avhich accomplish the reverse process, and by deoxidation 

 split up the oxides of nitrogen and cause a loss of nitrogen 

 from the soil. 



It must be confessed that our knowledge of these classes 

 of bacteria is very incomplete ; but it is fair to reason from 

 known facts that a well-drained, well-aerated soil promotes 

 the favoral)le or nitrifying process, and that an imdrained, 

 non-aerated soil, especially when heavily loaded with organic 

 matter, supplies the conditions for the unfavorable or deni- 

 trifying process. More than this we cannot say concerning 

 the farmer's ability to determine which process shall go on 

 in his soil. 



When we come to treat of those bacteria which associate 



